The present invention relates to an image output system for processing an input image signal from an image signal source to produce an output image signal for recording an image on an image recording medium.
There are known image output systems which process input image signals from various image signal sources such as television cameras, video discs, computer graphic systems, etc. so as to record visible images on image recording mediums. When an optimum image is to be recorded on an image recording medium, it is necessary to process the input image signal from the image signal source into an image signal adapted to the image output system and also to the characteristics of the image recording medium.
One conventional image output system which processes input image signals to meet such requirements is disclosed in Japanese Laid-Open Patent Publication No. 63-116855. The disclosed image output system has two look-up tables for image signal conversion. More specifically, the first look-up table converts an input image signal from an image signal source into an image signal adapted to the image output system, and the second look-up table converts the image signal into an image signal adapted to an image signal medium.
If the image recording medium is in the form of a photographic film which is coated with a photosensitive material, the amount of exposure to which the image recording medium is subjected is not linearly proportional to the brightness of an image which is produced on the image recording medium as a result of the exposure, and it is highly difficult to correct such a characteristic of the image recording medium using the second look-up table which effects only linear arithmetic operations with respect to the amount of exposure. The above characteristic of the image recording medium varies depending on cyan, magenta, and yellow which are colors to produce colored images. Therefore, if the characteristics of the image recording medium with respect to these colors are not accurately corrected, the gray balance of a reproduced colored image is poor. It is also difficult to correct image signals for a colored image on an image recording medium in view of human visual characteristics because the human visual characteristics are substantially linear to the logarithm of the amount of exposure to which the image recording medium is subjected.